1. Field of the Invention
The present invention relates broadly to methods of producing recombinant proteins. More specifically, the present invention concerns a method of producing recombinant proteins, or polypeptides, in bacteria or other host cells grown on a substantially solid, i.e., solid or semi-solid, nutrient growth medium harboring DNA sequences of interest for encoding the recombinant proteins under the control of an inducer-regulated promoter or constitutive promoter.
2. Background of the Invention
The majority of recombinant proteins, or polypeptides, currently available are produced from bacteria. Escherichia coli (hereinafter “E. coli”) is by far the most frequently used organism for recombinant protein production due to its relatively lenient nutrient requirements and fast growth rate. The prior art production process, shown in FIG. 1, uses liquid media and large-scale fermentation to yield high volumes of the bacteria. Unfortunately, efficient production of recombinant proteins in bacteria, both at the diagnostic and commercial level, remains a major problem for a number of reasons including that not all recombinant proteins can be expressed to a high level with a single technology. Other obstacles include the need for expensive equipment and large culture volumes; expensive induction due to the large culture volumes; difficulty controlling pH levels and temperatures; substrate inhibition; limited oxygen transfer which results in a need for pure oxygen which is expensive and increases overall production costs; plasmid instability and loss of recombinant protein production; the presence of relatively high levels of IPTG in the cultivation medium which leads to the inhibition of the growth of the E. coli cells; large volumes of waste water; and difficulty in consistently reproducing batch quality. The prior art fermentation process also leads to the formation and accumulation of growth inhibiting byproducts such as acetate, a lipophilic agent that is detrimental to cell growth, which reduce growth rate and biomass yield and repress the synthesis of DNA, RNA, protein, and lipids (Jensen, E. B., and S. Carlsen. 1990 Biotechnol, Bioeng. 36: 1-11).
Due to these and other problems and limitations in the prior art, an improved method of producing recombinant proteins is needed.